Create a custom modifier key to write special characters

Question

I have a Macbook with a Japanese keyboard, but don't need to write Japanese. I do prefer a US layout, but need to write German characters (äöüÄÖÜß). On Windows they had a "US - International" layout for this, where you can use for example AltGr+p for ö, AltGr+q for ä and so on.

I know I can do this on Mac by pressing Option + u then press a for ä, but this is too slow to type fast with.

Is there a way for me to create this using a custom modifier? I'd like to make the かな key right of the space bar a modifier key. So I'd press かな + p to get ö for example.

I have remapped a few keys on my keyboard via hidutil, for example to extend the right shift and backspace to the character left of it. But can't find a way to press multiple keys to type one character

Answer 1

Apple's input source US International PC may do what you want as it is. Below is the layout for a JIS keyboard. Umlauts are made by pressing Shift on the orange key and then the base letter.

In any case it would be easy to make something closer with Ukelele.

Here is a version I made a few years ago which conforms to Windows US International's Option level.